Method for determining a resultant image, computer program, machine-readable data carrier and imaging device

ABSTRACT

In an embodiment of the invention, a plurality of images of a region under examination are recorded at different times. Anatomical information and flow information are derived from the images. The anatomical information may relate to the course of vessels or the structure of perfused tissue. The temporal component of the flow information can advantageously be combined with the anatomical information in a resultant image. An intensity-dependent fenestration assigns a gray-scale value to pixels of the resultant image in accordance with the anatomical information. A time-dependent fenestration assigns a chromaticity to the pixels of the resultant image in accordance with the flow information and the gray-scale values and the chromaticities are assigned independently of one another. Intensity-dependent fenestration is combined with time-dependent fenestration so that chromaticities and gray-scale values are independent of one another and the anatomical information and the flow information are depicted undistorted in the resultant image.

PRIORITY STATEMENT

The present application hereby claims priority under 35 U.S.C. §119 toGerman patent application number DE 102014223658.4 filed Nov. 20, 2014,the entire contents of which are hereby incorporated herein byreference.

FIELD

At least one embodiment of the invention generally relates to a methodfor determining a resultant image, a computer program, amachine-readable data carrier and/or an imaging device.

BACKGROUND

Imaging devices, such as an X-ray device or a tomographic device enablethe recording of images of a region under examination at differenttimes. A comparison of the images enables information with a temporalcomponent to be derived from these images. The images generallyrepresent a volume and can include a plurality of prespecifiable slicesof the region under examination. If a substance flows through the regionunder examination, it is also possible to derive flow information fromthe images. Thus, modern imaging devices enable the identification ofdisorders of the blood flow in organs, for example the heart or thebrain. The most important methods for imaging measurements of the bloodflow include angiography and tomography perfusion scanning.

Therefore, the evaluation of the images requires the evaluation of bothanatomical information and flow information. Anatomical informationrelates to the anatomical structure of the region under examination andhence has a spatial component. Flow information relates to the dynamicsof a substance flowing in the region under examination and hence hasboth a spatial and a temporal component. The depiction of spatial andtemporal information for an imaging measurement is typically performedin that an image stack with a plurality of slices is compiled for eachtime point. The spatial and temporal information can then be depicted inthat individual slices or projections of the image stack are output as atemporally sequential sequence. Hence, this enables the evaluation ofthe temporal development of a substance flowing in the region underexamination. However, this is time-consuming and above alldisadvantageous for documentation.

To simplify the processing of spatial and temporal information, the U.S.Pat. No. 6,650,928 B1 suggests the conversion of tomographic images intocolor-coded maps. For example, two images of brain structures areoverlaid. This involves the overlaying of a colored, parametric imageover an anatomical image. The transparency of the overlaid image isadjustable to allow more or less of the anatomical structure to be seen.The drawback of this method is that good visibility of the anatomicalinformation impairs the visibility of the parametric information.

SUMMARY

An embodiment of the invention discloses how flow information with atemporal component can be advantageously combined with anatomicalinformation.

An embodiment of the invention is directed to a method. An embodiment ofthe invention is directed to a computer program. An embodiment of theinvention is directed to a machine-readable data carrier. An embodimentof the invention is directed to an imaging device.

Any features, advantages or alternative embodiments can be transferredto the other claimed subject matter and vice versa. In other words, thesubject-matter claims (which are, for example, directed toward a device)can also be developed with the features described or claimed inconnection with a method. The corresponding functional features of themethod are embodied by corresponding representational modules.

An embodiment of the invention is based on the recording of a pluralityof images of a region under examination at different times. In addition,anatomical information and flow information are derived from the images.In particular, the anatomical information can relate to the course ofvessels or the structure of perfused tissue. The inventors have nowidentified that the temporal component of the flow information can beadvantageously combined with the anatomical information in a resultantimage, wherein intensity-dependent fenestration can assign a gray-scalevalue to pixels of the resultant image in accordance with the anatomicalinformation, wherein time-dependent fenestration assigns a chromaticityto the pixels of the resultant image in accordance with the flowinformation and wherein the gray-scale values and the chromaticities areassigned independently of one another.

An embodiment of the invention is directed to a method for determining aresultant image, comprising:

recording a plurality of images of a region under examination atdifferent times;

deviating anatomical information from at least one of the plurality ofimages;

subsequently deviating flow information from the at least one of theplurality of images; and

determining a resultant image, wherein an intensity-dependentfenestration assigns gray-scale values to pixels of the resultant imagein accordance with the deviated anatomical information, wherein atime-dependent fenestration assigns chromaticities to the pixels inaccordance with the flow information and wherein the gray-scale valuesand the chromaticities are assigned independently of one another.

An embodiment of the invention also relates to a computer program with aprogram code for performing all method steps of an embodiment of theabove-mentioned aspects of the invention when the computer program isexecuted in the computer. This enables the method to be executedreproducibly and with less susceptibility to error on differentcomputers.

An embodiment of the invention also relates to a machine-readable datacarrier on which the above-described computer program is stored.

An embodiment of the invention also relates to an imaging device with acomputer for controlling the imaging device, wherein, by sendingcommands to the imaging device, the computer causes the imaging deviceto execute a method of the above-mentioned aspects of an embodiment ofthe invention.

The computer can also be embodied for controlling the imaging devicesuch that, by sending commands to the imaging device, causes thetomography device to perform a method according to an embodiment of theinvention.

An imaging device can be a magnetic resonance tomography device. In thiscase, the radiation comprises a radio-frequency alternating field in theradio-frequency range. In this case, the radiation source is at leastone coil for generating the radio-frequency alternating field. Inmagnetic resonance tomography, the radiation detector is at least onecoil for the detection of radio-frequency radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

The following describes and explains the invention in more detail withreference to the example embodiments shown in the figures.

The figures show:

FIG. 1 an imaging device,

FIG. 2 a schematic view of a resultant image with individual pixels,

FIG. 3 a schematic view of a resultant image with different regions,

FIG. 4 a flow diagram of a method according to an embodiment of theinvention.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

The drawings are to be regarded as being schematic representations andelements illustrated in the drawings are not necessarily shown to scale.Rather, the various elements are represented such that their functionand general purpose become apparent to a person skilled in the art. Anyconnection or coupling between functional blocks, devices, components,or other physical or functional units shown in the drawings or describedherein may also be implemented by an indirect connection or coupling. Acoupling between components may also be established over a wirelessconnection. Functional blocks may be implemented in hardware, firmware,software, or a combination thereof.

Various example embodiments will now be described more fully withreference to the accompanying drawings in which only some exampleembodiments are shown. Specific structural and functional detailsdisclosed herein are merely representative for purposes of describingexample embodiments. The present invention, however, may be embodied inmany alternate forms and should not be construed as limited to only theexample embodiments set forth herein.

Accordingly, while example embodiments of the invention are capable ofvarious modifications and alternative forms, embodiments thereof areshown by way of example in the drawings and will herein be described indetail. It should be understood, however, that there is no intent tolimit example embodiments of the present invention to the particularforms disclosed. On the contrary, example embodiments are to cover allmodifications, equivalents, and alternatives falling within the scope ofthe invention. Like numbers refer to like elements throughout thedescription of the figures.

Before discussing example embodiments in more detail, it is noted thatsome example embodiments are described as processes or methods depictedas flowcharts. Although the flowcharts describe the operations assequential processes, many of the operations may be performed inparallel, concurrently or simultaneously. In addition, the order ofoperations may be re-arranged. The processes may be terminated whentheir operations are completed, but may also have additional steps notincluded in the figure. The processes may correspond to methods,functions, procedures, subroutines, subprograms, etc.

Specific structural and functional details disclosed herein are merelyrepresentative for purposes of describing example embodiments of thepresent invention. This invention may, however, be embodied in manyalternate forms and should not be construed as limited to only theembodiments set forth herein.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of example embodiments of thepresent invention. As used herein, the term “and/or,” includes any andall combinations of one or more of the associated listed items. Thephrase “at least one of” has the same meaning as “and/or”.

Further, although the terms first, second, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,it should be understood that these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areused only to distinguish one element, component, region, layer, orsection from another region, layer, or section. Thus, a first element,component, region, layer, or section discussed below could be termed asecond element, component, region, layer, or section without departingfrom the teachings of the present invention.

Spatial and functional relationships between elements (for example,between modules) are described using various terms, including“connected,” “engaged,” “interfaced,” and “coupled.” Unless explicitlydescribed as being “direct,” when a relationship between first andsecond elements is described in the above disclosure, that relationshipencompasses a direct relationship where no other intervening elementsare present between the first and second elements, and also an indirectrelationship where one or more intervening elements are present (eitherspatially or functionally) between the first and second elements. Incontrast, when an element is referred to as being “directly” connected,engaged, interfaced, or coupled to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between,” versus “directly between,” “adjacent,” versus“directly adjacent,” etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments of the invention. As used herein, the singular forms “a,”“an,” and “the,” are intended to include the plural forms as well,unless the context clearly indicates otherwise. As used herein, theterms “and/or” and “at least one of” include any and all combinations ofone or more of the associated listed items. It will be furtherunderstood that the terms “comprises,” “comprising,” “includes,” and/or“including,” when used herein, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

It should also be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which example embodiments belong. Itwill be further understood that terms, e.g., those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,“upper”, and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, term such as “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein are interpreted accordingly.

Portions of the example embodiments and corresponding detaileddescription may be presented in terms of software, or algorithms andsymbolic representations of operation on data bits within a computermemory. These descriptions and representations are the ones by whichthose of ordinary skill in the art effectively convey the substance oftheir work to others of ordinary skill in the art. An algorithm, as theterm is used here, and as it is used generally, is conceived to be aself-consistent sequence of steps leading to a desired result. The stepsare those requiring physical manipulations of physical quantities.Usually, though not necessarily, these quantities take the form ofoptical, electrical, or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise, or as is apparent from the discussion,terms such as “processing” or “computing” or “calculating” or“determining” of “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computingdevice/hardware, that manipulates and transforms data represented asphysical, electronic quantities within the computer system's registersand memories into other data similarly represented as physicalquantities within the computer system memories or registers or othersuch information storage, transmission or display devices.

An embodiment of the invention is based on the recording of a pluralityof images of a region under examination at different times. In addition,anatomical information and flow information are derived from the images.In particular, the anatomical information can relate to the course ofvessels or the structure of perfused tissue. The inventors have nowidentified that the temporal component of the flow information can beadvantageously combined with the anatomical information in a resultantimage, wherein intensity-dependent fenestration can assign a gray-scalevalue to pixels of the resultant image in accordance with the anatomicalinformation, wherein time-dependent fenestration assigns a chromaticityto the pixels of the resultant image in accordance with the flowinformation and wherein the gray-scale values and the chromaticities areassigned independently of one another.

An advantage of an embodiment of the invention is justified in thatintensity-dependent fenestration is combined with time-dependentfenestration so that chromaticities and gray-scale values areindependent of one another. This is because this means that theintensity-dependent fenestration does not influence the time-dependentfenestration. This enables anatomical information and flow informationto be displayed undistorted in the resultant image. The recording of theimages is a physical measurement and the anatomical information and flowinformation derived are measuring results corresponding to a physicalstructure. Therefore, the invention has the technical effect thatmeasuring results corresponding to a physical measurement can becombined with one another without the risk of distortion in a resultantimage. Therefore, the resultant image according to the invention has aparticularly high information content.

In this case, the anatomical information can be embodied as a spatialintensity distribution derived from at least one of the images. The flowinformation can be embodied as a distribution of flow values derivedfrom the images. The flow values are, for example, a parametercharacterizing a physical process, in particular a movement. The flowinformation is typically derived on the basis of a change in thedistribution of intensity values of the images recorded at differenttimes. In this case, the flow information can be determined such that avalue of its own, in particular a flow value, is determined for eachpixel of the resultant image.

If the region under examination is a body part or an organ of a patient,the flow information can be derived specifically for the patient. Theresultant image then has a particularly high diagnostic value.

The independent assignment of gray-scale values and chromaticities canin particular include the independent assignment of gray-scale valuesand color shades since the color shade is particularly well suited to beperceived as information independent of the gray-scale value. Theindependent assignment can also be performed in that the chromaticity,in particular the color shade, is orthogonal to the gray-scale value. Inthis case, the time-dependent fenestration is based on a color space inwhich the chromaticity, in particular the color shade, and thegray-scale value are orthogonal to one another.

According to a further aspect of an embodiment of the invention, therecording of at least a part of the images is contrast-medium-supported.This enables the flow information also to include information on theinflow of contrast medium, in particular in a blood vessel. The imagescan then be recorded in the form of angiography images or tomographyperfusion images so that it is particularly easy to derive flowinformation relating to the blood flow in the region under examination.

According to a further aspect of an embodiment of the invention, theanatomical information is derived in that a first projection takes placevia a plurality of the images recorded at different times. Therefore,the first projection at least takes place along the time axis. Forexample, a particularly large number of measuring points is taken intoaccount during the first derivation of the anatomical information. Thismeans the information content of the resultant image is particularlyhigh. It is also possible to increase reliability during a furtheranalysis on the basis of the resultant image.

According to a further aspect of an embodiment of the invention, theflow information is derived on the basis of a physical model. Forexample, the physical model can describe the propagation of blood in ablood vessel or the propagation of blood in a tissue. In particular, thetissue can be highly capillarized. The physical model can also describethe propagation of a substance by diffusion. This aspect of theinvention enables the flow information to be determined particularlyaccurately.

In addition to the chromaticity, a color possesses the properties ofluminance and color saturation. A color can be depicted in differentcolor spaces such as, for example, the red-green-blue (RGB) color space,the L*a*b color space, the CIE standard color table or the HSV (hue,saturation, value) color space. The axes, which span a color space, canalso be generally described as channels of a color space. With temporalfenestration, in particular a color shade can correspond directly toflow information. In order to ensure that the information content of theresultant image is particularly high and both the anatomical informationand the flow information are reproduced undistorted, it is also possibleto place requirements on the luminance or color saturation.

According to a further aspect of an embodiment of the invention,time-dependent fenestration is performed such that a maximum luminanceof the chromaticities for the pixels is the same. Since the luminancecorresponds to a gray-scale value, this means that the maximumgray-scale value for the pixels is also the same. This excludes thepossibility of pixels to which different chromaticities and the samegray-scale values are assigned nevertheless having different luminancevalues or gray-scale values. This in particular enablesintensity-dependent fenestration to be performed in effect linearly,that is also taking account of the time-dependent fenestration.

According to a further aspect of an embodiment of the invention,time-dependent fenestration is performed such that the maximum colorsaturation for the pixels is the same. For example, the color saturationcan be determined in the CIE standard color table as a relative distancefrom the neutral point. In the HSV color space, color saturation istreated as one of the three spanning axes. If the maximum colorsaturation for the pixels is now the same, the assignment of thegray-scale values changes the corresponding chromaticities in a similarand regular way.

According to a further aspect of an embodiment of the invention, thegray scale for the intensity-dependent fenestration and/or the colorscale for the time-dependent fenestration can be prespecified. Thismakes the invention particularly flexible. For example, the maximumluminance of the chromaticities or the maximum color saturation can beprespecified. In particular, the gray scale and/or the color scale canbe selected by a user, for example by means of a graphical userinterface.

According to a further aspect of an embodiment of the invention, thegraphical output of the resultant image is depicted on a display unit,wherein a section of the resultant image can be selected, wherein thegray scale and/or the color scale are dependent upon the sectionselected. For example, the gray scale can be adjusted to the anatomicalinformation derived for the section or the color scale to the flowinformation derived for the section. To this end, the contrast of thesection is increased which facilitates the further analysis of thissection.

The images can in principle be either two-dimensional projections orimage stacks calculated from tomographic recordings with a plurality ofslices. An image of this kind recorded at a time point can also bedescribed as a spatially three-dimensional image. The sectional planesfor calculating the individual slices of the image stack can inprinciple be freely selectable. The images recorded and the resultantimage can have the same spatial dimensions. However, the images recordedand the resultant image can have different spatial dimensions. With aparticularly important aspect of the invention, the images are eachspatially three-dimensional images, wherein the anatomical informationand the flow information are both embodied as spatiallythree-dimensional and wherein the resultant image is a spatiallytwo-dimensional image.

According to this aspect of an embodiment of the invention,intensity-dependent fenestration is performed such that the gray-scalevalues are assigned to the pixels in accordance with the anatomicalinformation projected along a spatial direction, wherein thetime-dependent fenestration is performed such that the chromaticitiesare assigned to the pixels in accordance with the blood flow informationprojected along the spatial direction. The spatial direction can befreely selectable or it can also be prespecified by a preferred axis ofthe region under examination. In particular, the spatial direction canbe a body axis of the patient, for example perpendicular to the sagittalplane, perpendicular to the frontal plane or perpendicular to thetransversal plane. This enables the combination of a particularly largeamount of spatial and temporal information in the resultant image.

An embodiment of the invention also relates to a computer program with aprogram code for performing all method steps of an embodiment of theabove-mentioned aspects of the invention when the computer program isexecuted in the computer. This enables the method to be executedreproducibly and with less susceptibility to error on differentcomputers.

An embodiment of the invention also relates to a machine-readable datacarrier on which the above-described computer program is stored.

An embodiment of the invention also relates to an imaging device with acomputer for controlling the imaging device, wherein, by sendingcommands to the imaging device, the computer causes the imaging deviceto execute a method of the above-mentioned aspects of an embodiment ofthe invention.

The computer can also be embodied for controlling the imaging devicesuch that, by sending commands to the imaging device, causes thetomography device to perform a method according to an embodiment of theinvention.

An imaging device can be a magnetic resonance tomography device. In thiscase, the radiation comprises a radio-frequency alternating field in theradio-frequency range. In this case, the radiation source is at leastone coil for generating the radio-frequency alternating field. Inmagnetic resonance tomography, the radiation detector is at least onecoil for the detection of radio-frequency radiation.

The imaging device can also be an X-ray device which is configured torecord a plurality of X-ray projections from different projectionangles. For example, an X-ray device of this kind is a computertomography device with an annular rotating frame or a C-arm X-raydevice. The recordings can be generating during a, in particularcontinuous, rotational movement of a recording unit with an X-ray sourceand an X-ray detector interacting with the X-ray source. The X-raysource can in particular be an X-ray tube with a rotary anode. An X-raydetector for a computer tomography device is, for example, a linedetector with a plurality of lines. An X-ray detector for a C-arm X-raydevice is, for example, a flat detector. The X-ray detector can beembodied as both energy-resolving and metering.

FIG. 1 shows an imaging device using the example of a computedtomography device. The computed tomography device shown has a recordingunit 17 comprising a radiation source 8 in the form of an X-ray sourceand a radiation detector 9 in the form of an X-ray detector. During therecording of X-ray projections, the recording unit 17 rotates about asystem axis 5 and, during the recording, the X-ray source emits rays 2in the form of X-rays. In the example shown here, the X-ray source is anX-ray tube. In the example shown here, the X-ray detector is a linedetector with a plurality of lines.

In the example shown here, during the recording of projections, apatient 3 lies on a patient bed 6. The patient bed 6 is connected to abed base 4 such that the base bears the patient bed 6 with the patient3. The patient bed 6 is designed to move the patient 3 along a recordingdirection through the opening 10 in the recording unit 17. The recordingdirection is as a rule determined by the system axis 5 about which therecording unit 17 rotates during the recording of X-ray projections. Inthe case of a spiral recording, the patient bed 6 is moved continuouslythrough the opening 10 while the recording unit 17 rotates about thepatient 3 and records X-ray projections. As a result, the X-raysdescribe a spiral on the surface of the patient 3.

In addition, a tomographic device can also have a contrast-mediuminjector for the injection of contrast medium into the blood circulationof the patient 3. This enables the images to be recorded withcontrast-medium support such that structures located in the region underexamination, in particular blood vessels, can be depicted with enhancedcontrast. The contrast-medium injector also provides the option ofactuating angiography recordings or performing perfusion scanning.Contrast media should be generally understood to mean media that improvethe depiction of body structures and functions during the imagingmethod. For the purposes of the present application, contrast mediashould be understood to be both conventional contrast media, such as,for example, iodine or gadolinium, and tracers, such as, for example.18F, 11C, 15O or 13N.

The imaging device shown here comprises a computer 12 connected to adisplay unit 11 and an input unit 7. The display unit 11 can, forexample, be an LCD, plasma or OLED screen. It can also be atouch-sensitive screen which is also embodied as an input unit 7. Atouch-sensitive screen of this kind can be integrated in the imagingdevice or embodied as part of a mobile device. The display unit 11 issuitable for inventive graphical output OUT of the resultant image. Theinput unit 7 is, for example, a keyboard, a mouse, a so-called “touchscreen” or even a microphone for voice input. The input unit 7 is alsosuitable to select a section of the resultant image output on thedisplay unit 11.

The computer 12 comprises a reconstruction unit 14 for thereconstruction of an image from raw data. For example, thereconstruction unit 14 can reconstruct a tomographic image in the formof an image stack with a plurality of slices. The imaging device canalso have a computing unit 15. The computing unit 15 can interact with acomputer-readable data carrier 13, in particular in order to carry out amethod according to the invention by means of a computer program with aprogram code. The computer program can also be stored in retrievableform on the machine-readable carrier. In particular, themachine-readable carrier can be a CD, DVD, blu-ray disk, a memory stickor a hard disk. Both the computing unit 15 and the reconstruction unit14 can be embodied in the form of hardware or in the form of software.For example, the computing unit 15 or the reconstruction unit 14 isembodied as a so-called FPGA (“field programmable gate array”) orcomprises an arithmetic logic unit.

In the embodiment shown here, at least one computer program is stored onthe memory of the computers 12, wherein this program carries out all themethod steps of the method according to the invention when the computerprogram is executed on the computer 12. The computer program forexecuting the method steps of the method according to the inventioncomprises a program code. The computer program can also be embodied asan executable file and/or on another computing system instead of thecomputer 12. For example, the imaging device can be designed such thatthe computer 12 loads the computer program for the execution of themethod according to the invention into its internal working memory viaan intranet or the internet.

FIG. 2 shows a schematic view of a resultant image with individualpixels. In the example shown here, the circles each depict a pixel 16 ofthe resultant image. The pixels 16 can be both pixels and voxels. Here,‘pixels’ designates pixels 16 of a spatially two-dimensional image,‘voxels’ designates the pixels 16 of a spatially three-dimensionalimage. The images for the determination of the resultant image can berecorded with a tomography device described in FIG. 1 and outputgraphically on the display unit 11.

The filling of the individual circles indicates the gray-scale valueassigned to a pixel 16 by intensity-dependent fenestration. In themethod according to the invention, this gray-scale value alsocorresponds to the luminance 19 assumed by the chromaticity of aspecific resultant image. Accordingly, in the resultant image shownhere, the luminance 19 falls going from left to right. In addition, allthe pixels 16 in one column are of equal luminance. The directions ofthe arrows 20 associated with the circles each indicate thechromaticity. For example, the color scale for time-dependentfenestration is based on the rainbow scale. Accordingly, an arrow 20oriented toward the right can correspond to a red shade, an arrow 20oriented downward to a green shade and a 20 arrow oriented toward theleft to a blue shade. Therefore, in the example shown here, a rainbowscale is scanned from top to bottom. In the example shown here, themaximum luminance is the same for all chromaticities. In this example,the maximum luminance is indicated by a white-filled circle. The lengthsof the arrows 20 indicate the degree of the color saturation in eachcase. A longer arrow 20 corresponds to stronger color saturation. In theexample shown here, the color scale is selected such that there is adirect relationship between the color saturation and the luminance 19,at least for the pixels 19 to which a colorful color shade is assigned.Desaturation takes place from left to right wherein the desaturationtakes the form of an increasing proportion of black. I.e. a white-filledcircle corresponds to a pixel 6 to which maximum saturation has beenassigned. On the other hand, a white-filled circle corresponds to apixel 16 to which minimum saturation has been assigned so that thecorresponding pixel 16 appears black. Therefore, in certain embodimentsof the invention, the color saturation can be determined as a functionof the luminance 19 or of the assigned grey-scale value. In the exampleshown here, there is complete desaturation with a normalized luminance19 of greater than zero. In another example (not shown here,)desaturation takes place by means of an increasing proportion of white.

Intensity-dependent fenestration is performed in accordance with theanatomical information. The anatomical information can in particular bedescribed by an intensity distribution. The anatomical information andhence also an intensity distribution can be derived with known imageprocessing methods from at least one of the images recorded. Forexample, the first derivation of the anatomical information includesfiltering or segmentation of at least one of the images recorded. Theanatomical information can also be described in a slice image of aregion under examination reconstructed from a tomography recording fromthe distribution from intensity values in Hounsfield units.Intensity-dependent fenestration can be described by the expressionshown below for 1(c), wherein c indicates the intensity in Hounsfieldunits and c_max and c_min respectively the maximum and the minimumintensity within the intensity distribution in Hounsfield units. Idesignates the assigning gray-scale value, I_max and I_min respectivelydesignate the maximum and minimum gray-scale values that can be assignedto a pixel 16 with intensity-dependent fenestration. For example,I_min=0 and I_max=255 is possible.

${I(c)} = \begin{Bmatrix}{I\_ min} & {c \leq {c\_ min}} \\{{I\_ min} + {\left( {{I\_ max} - {I\_ min}} \right)*{\left( {c - {c\_ min}} \right)/\left( {{c\_ max} - {c\_ min}} \right)}}} & \; \\{I\_ max} & {c \geq {c\_ max}}\end{Bmatrix}$

Time-dependent fenestration is performed in accordance with flowinformation. The flow information is derived from the images, inparticular, the flow information can be derived from changes in adistribution of intensity values between images recorded at differenttime points. In this context, the flow information has a temporalcomponent. For example, the flow information can be information relatingto the blood flow. In particular, this can be the blood volume, theaverage flow rate through a volume within the region under examinationand the delay time until the maximum inflow of contrast medium in theregion under examination. In different embodiments of the invention, theflow information can relate to both a directed flow and an undirectedflow. In one embodiment of the invention, the flow information isdiffusion parameters in the region under examination. The diffusionparameters usually relate to the diffusion of water and can inparticular be derived on the basis of diffusion tensor imaging.

The flow information can relate directly to a temporal value or the flowinformation is derived on the basis of a time-dependent phenomenon. Forexample, rates or diffusion Parameters are derived from a time-dependentphenomenon, namely from a movement. The flow information can naturallyalso have spatial component in that it corresponds to a spatialdistribution. The time-dependent fenestration causes scaling of the flowinformation on the basis of the time-dependent component. For example,the time-dependent fenestration can be described by the expression shownbelow for L(t), wherein t specifies a through-flow time and t_max andt_min the respective maximum and minimum through-flow times. Ldesignates the assigning chromaticity, L_max and L_min designate therespective maximum and minimum chromaticity within a color scale whichcan be assigned to a pixel 16 during intensity-dependent fenestration.

${L(t)} = \begin{Bmatrix}1 & {t \leq {t\_ min}} \\{1 + {\left( {{L\_ max} - 1} \right)*{\left( {t - {t\_ min}} \right)/\left( {{t\_ max} - {t\_ min}} \right)}}} & \; \\{L\_ max} & {t \geq {t\_ max}}\end{Bmatrix}$

During temporal fenestration, it is also possible to label the pixels 16to which no valid flow information can be assigned. For example, therecannot be any valid flow information if the noise in the respectivepixel 16 exceeds a limit value. The labeling can be performed such thatthe pixels 16 to which no valid flow information can be assigned areassigned no chromaticity or the chromaticity “white”. In such a case,L=0 can be selected. In this context, the time-dependent fenestrationcan include labeling.

It is generally applicable that a chromaticity can be assigned in that apixel 16 is assigned at least one value of one channel of a color space.For example, the chromaticity can be assigned in that the channel ‘Hue’in the HSV color space is assigned a value. It is also possible for thechromaticity to be assigned in that the channels ‘Red’, ‘Green’, ‘Blue’of the RGB color space are each assigned a value. In differentembodiments of the invention, the time-dependent fenestration includes avalue being assigned to a pixel 16 for each channel of a color space. Inaddition, the chromaticities can also be described in a normalized form.If the RGB color space is selected without restricting the generality,the normalized chromaticity is expressed as:

${{FW\_ norm}(i)} = \frac{\left\{ {{r\_ i},{g\_ i},{b\_ i}} \right\}}{3*{\max \left( {{r\_ i},{g\_ i},{b\_ i}} \right)}}$

Here, FW_norm(i) designates the normalized chromaticity. r_i, g_i andb_i designate the values of the channels ‘Red’, ‘Green’ and ‘Blue’.Here, i specifies the index of the color space, for example, i can bebetween 0 and 255 with a color space with 255 color shades. The functionmax(r_i, g_i, b_i) specifies the maximum value of the three channels forthe index i. In one embodiment of the invention, the time-dependentfenestration is such that the maximum luminance 19 of the chromaticitiesfor the pixels 16 is the same. In the RGB color space, the luminance 19is specified by H(i)=r_i+g_i+b_i, wherein H designates the luminance 19.It is now therefore possible to select the color scale such that themaximum luminance 19 is the same for all the assigned chromaticities. Inparticular, the maximum normalized luminance 19 of the chromaticitiesfor the pixels 16 can be the same. In the RGB color space, thenormalized, maximum luminance of the chromaticities is specified by thefollowing expression:

${{L\_ max}\left( {{FW\_ norm}(i)} \right)} = \frac{{r\_ i} + {g\_ i} + {b\_ i}}{3*{\max \left( {{r\_ i},{g\_ i},{b\_ i}} \right)}}$

Here, L_max designates the normalized, maximum luminance which canassume different values in different embodiments of the invention. Forexample, the condition L_max=1 or L_max=0.5 can be fulfilled.

It is now possible to combine the intensity-dependent and thetime-dependent fenestration with one another. In the example of the RGBcolor space, the combined fenestration is then specified by thefollowing expression:

${\left\{ {R,G,B} \right\} {\_ l}},{m = \begin{Bmatrix}{{I\left( {{MC\_ l},m} \right)}*{\left\{ {1,1,1} \right\}/3}} & {{{wenn}\mspace{14mu} {L\left( {{t\_ l},m} \right)}} = 0} \\{{I\left( {{MC\_ l},m} \right)}*{FW\_ norm}\left( {L\left( {{t\_ l},m} \right)} \right)} & \;\end{Bmatrix}}$

In this case, 1 and m represent the two-dimensional position of therelevant pixel 16 in the resultant image, which comprises 1 lines and mcolumns. In this example, t_1,m designates the flow information in theform of a through-flow time assigned to a pixel 16. MC_1,m designate thedistribution of the anatomical information determined, for example, by aprojection of the maximum intensity beyond the times of the imagesrecorded. * designates a multiplication. The expression {1,1,1} is aunit vector in the RGB color space. The unit vector of the respectivecolor space used can be used in further embodiments of the invention.

The gray-scale value I can therefore be dependent on the distribution ofthe anatomical information. The color space can, as described here byway of example, be constructed such that

the gray-scale value for pixels of the resultant image, to which nochromaticity, in particular no colorful chromaticity, is assigned ismultiplied with the unit vector of the color space,

the gray-scale value for pixels of the resultant image, to which achromaticity, in particular a colorful chromaticity, is assigned, ismultiplied with the respective, normalized chromaticity assigned.

Therefore, the gray-scale value and chromaticity are independent of oneanother in such a color space. Hence, the color space can also beconstructed such that the gray-scale value and chromaticity areorthogonal to one another. The color space can also be constructed suchthat it does not include the chromaticities “white” and “black”, butonly colorful colors.

FIG. 3 is a schematic view of a resultant image with different regions.In the example shown here, the resultant image shown in the schematicview is a two-dimensional image of a brain of a patient 3. This shows aprojection of the brain along the long body axis of the patient 3 sothat the front side in FIG. 3 points upward. FIG. 3 is drawn in stronglyschematic form and does not show any anatomical details. The firstregion 21 of the resultant image is characterized in that nochromaticity is assigned to the pixels 16 in the first region 21 or thechromaticity is equal to zero. For example, the first region 21 can befurther characterized in that that the flow information, in particularits temporal component, cannot be determined with a specific accuracy.Therefore, it may be advisable also not to assign any chromaticity tocertain pixels 16 during time-dependent fenestration when the expectederror in the chromaticity exceeds a limit value. For example, theexpected error can be high due to a high noise level in the imagesrecorded. In the example shown here, there are no large blood vessels inthe first region 21 so that, with images recorded with contrast medium,the measurable intensity in the images is too low for the temporalinformation to be derived with a high degree of accuracy. On the otherhand, in the second region 22, a chromaticity is assigned to each of thepixels 16 by the time-dependent fenestration. This is because, theexpected chromaticity error in the second region 22 is below a limitvalue. In the example shown here, there are large blood vessels in thesecond region 22 so that, with images recorded with contrast medium, themeasurable intensity in the images is sufficient for the temporalinformation to be derived with a high degree of accuracy. For purposesof clarity, the second region 22 in FIG. 3 is shown with hatching andthe first region 21 is depicted in FIG. 3 in a uniform gray-scale value.In FIG. 3, the different chromaticities in the second region 22 areindicated by the orientation of the hatching. The luminance of therespective chromaticity is depicted by the density of the hatching. Inthe example shown, the flow information is the arrival time of acontrast medium.

FIG. 4 is a flow diagram of a method according to the invention. Therecording RED of a plurality of images of a region under examination atdifferent times is performed by an imaging device. In this case, theimages can be recorded with an identical or variable temporal interval.In particular, it is of advantage for the derivation of perfusionparameters for a plurality of images with an identical temporal intervalto be recorded. The first derivation D-1 of anatomical information fromat least one of the images and the second derivation D-2 of flowinformation from the images can be supported by a computer 12 and takeplace automatically. The method depicted here also includes the step ofthe determination IMG of a resultant image, wherein anintensity-dependent fenestration assigns pixels 16 of the resultantimage gray-scale values in accordance with the anatomical information,wherein a time-dependent fenestration assigns the pixels 16chromaticities in accordance with the flow information and wherein thegray-scale values and the chromaticities are assigned independently ofone another. The method shown here also includes the step of thegraphical output OUT of the resultant image on a display unit 11,wherein a section of the resultant image can be selected, wherein thegray scale and/or the color scale are dependent upon the selectedsection.

In a further embodiment of the invention, the flow information isderived on the basis of a physical model. The flow information can inparticular be derived such that in particular a flow value is determinedfor each pixel of the resultant image based on the physical model. Amodel of this kind can in particular model the flow of a substance andat the same time also take account of properties of the substance and astructure limiting the flowing substance. For example, the model canmodel the blood flow in a blood vessel or in tissue penetrated by bloodvessels. The flow information can also be derived on the basis of aphysical model such that the model can be adapted to the change in thedistribution of intensity values. The adaptation can in particular takeplace by the interpolation of intensity values at different times. Inthis case, a parameter can be adapted to the change in the distributionof intensity values, in particular a parameter characterizing a physicalprocess. It is also possible for the change in the distribution ofintensity values to be interpolated.

The flow information can also be derived on the basis of a physicalmodel such that a simulation is performed. For example, this is anumerical simulation, which can also be embodied as a flow simulation. Aflow simulation of this kind can in particular be embodied in the formof a so-called CFD simulation (CFD is an abbreviation for computationalfluid dynamics). The flow simulation can also be based on or moreanatomical parameters, which are derived from at least one of the imagesrecorded at different times. The anatomical parameter can, for example,be the diameter of a blood vessel. The enables the flow information tobe determined particularly accurately on the one hand and yetpatient-specifically on the other.

The aforementioned description is merely illustrative in nature and isin no way intended to limit the disclosure, its application, or uses.The broad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. It should be understood thatone or more steps within a method may be executed in different order (orconcurrently) without altering the principles of the present disclosure.Further, although each of the embodiments is described above as havingcertain features, any one or more of those features described withrespect to any embodiment of the disclosure can be implemented in and/orcombined with features of any of the other embodiments, even if thatcombination is not explicitly described. In other words, the describedembodiments are not mutually exclusive, and permutations of one or moreembodiments with one another remain within the scope of this disclosure.

The patent claims filed with the application are formulation proposalswithout prejudice for obtaining more extensive patent protection. Theapplicant reserves the right to claim even further combinations offeatures previously disclosed only in the description and/or drawings.

The example embodiment or each example embodiment should not beunderstood as a restriction of the invention. Rather, numerousvariations and modifications are possible in the context of the presentdisclosure, in particular those variants and combinations which can beinferred by the person skilled in the art with regard to achieving theobject for example by combination or modification of individual featuresor elements or method steps that are described in connection with thegeneral or specific part of the description and are contained in theclaims and/or the drawings, and, by way of combinable features, lead toa new subject matter or to new method steps or sequences of methodsteps, including insofar as they concern production, testing andoperating methods. Further, elements and/or features of differentexample embodiments may be combined with each other and/or substitutedfor each other within the scope of this disclosure and appended claims.

References back that are used in dependent claims indicate the furtherembodiment of the subject matter of the main claim by way of thefeatures of the respective dependent claim; they should not beunderstood as dispensing with obtaining independent protection of thesubject matter for the combinations of features in the referred-backdependent claims. Furthermore, with regard to interpreting the claims,where a feature is concretized in more specific detail in a subordinateclaim, it should be assumed that such a restriction is not present inthe respective preceding claims.

Since the subject matter of the dependent claims in relation to theprior art on the priority date may form separate and independentinventions, the applicant reserves the right to make them the subjectmatter of independent claims or divisional declarations. They mayfurthermore also contain independent inventions which have aconfiguration that is independent of the subject matters of thepreceding dependent claims.

Still further, any one of the above-described and other example featuresof the present invention may be embodied in the form of an apparatus,method, system, computer program, tangible computer readable medium andtangible computer program product. For example, of the aforementionedmethods may be embodied in the form of a system or device, including,but not limited to, any of the structure for performing the methodologyillustrated in the drawings.

In this application, including the definitions below, the term ‘module’or the term ‘controller’ may be replaced with the term ‘circuit.’ Theterm ‘module’ may refer to, be part of, or include processor hardware(shared, dedicated, or group) that executes code and memory hardware(shared, dedicated, or group) that stores code executed by the processorhardware.

The module may include one or more interface circuits. In some examples,the interface circuits may include wired or wireless interfaces that areconnected to a local area network (LAN), the Internet, a wide areanetwork (WAN), or combinations thereof. The functionality of any givenmodule of the present disclosure may be distributed among multiplemodules that are connected via interface circuits. For example, multiplemodules may allow load balancing. In a further example, a server (alsoknown as remote, or cloud) module may accomplish some functionality onbehalf of a client module.

Further, at least one embodiment of the invention relates to anon-transitory computer-readable storage medium comprisingelectronically readable control information stored thereon, configuredin such that when the storage medium is used in a controller of amagnetic resonance device, at least one embodiment of the method iscarried out.

Even further, any of the aforementioned methods may be embodied in theform of a program. The program may be stored on a non-transitorycomputer readable medium and is adapted to perform any one of theaforementioned methods when run on a computer device (a device includinga processor). Thus, the non-transitory, tangible computer readablemedium, is adapted to store information and is adapted to interact witha data processing facility or computer device to execute the program ofany of the above mentioned embodiments and/or to perform the method ofany of the above mentioned embodiments.

The computer readable medium or storage medium may be a built-in mediuminstalled inside a computer device main body or a removable mediumarranged so that it can be separated from the computer device main body.The term computer-readable medium, as used herein, does not encompasstransitory electrical or electromagnetic signals propagating through amedium (such as on a carrier wave); the term computer-readable medium istherefore considered tangible and non-transitory. Non-limiting examplesof the non-transitory computer-readable medium include, but are notlimited to, rewriteable non-volatile memory devices (including, forexample flash memory devices, erasable programmable read-only memorydevices, or a mask read-only memory devices); volatile memory devices(including, for example static random access memory devices or a dynamicrandom access memory devices); magnetic storage media (including, forexample an analog or digital magnetic tape or a hard disk drive); andoptical storage media (including, for example a CD, a DVD, or a flu-rayDisc). Examples of the media with a built-in rewriteable non-volatilememory, include but are not limited to memory cards; and media with abuilt-in ROM, including but not limited to ROM cassettes; etc.Furthermore, various information regarding stored images, for example,property information, may be stored in any other form, or it may beprovided in other ways.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes, datastructures, and/or objects. Shared processor hardware encompasses asingle microprocessor that executes some or all code from multiplemodules. Group processor hardware encompasses a microprocessor that, incombination with additional microprocessors, executes some or all codefrom one or more modules. References to multiple microprocessorsencompass multiple microprocessors on discrete dies, multiplemicroprocessors on a single die, multiple cores of a singlemicroprocessor, multiple threads of a single microprocessor, or acombination of the above.

Shared memory hardware encompasses a single memory device that storessome or all code from multiple modules. Group memory hardwareencompasses a memory device that, in combination with other memorydevices, stores some or all code from one or more modules.

The term memory hardware is a subset of the term computer-readablemedium. The term computer-readable medium, as used herein, does notencompass transitory electrical or electromagnetic signals propagatingthrough a medium (such as on a carrier wave); the term computer-readablemedium is therefore considered tangible and non-transitory. Non-limitingexamples of the non-transitory computer-readable medium include, but arenot limited to, rewriteable non-volatile memory devices (including, forexample flash memory devices, erasable programmable read-only memorydevices, or a mask read-only memory devices); volatile memory devices(including, for example static random access memory devices or a dynamicrandom access memory devices); magnetic storage media (including, forexample an analog or digital magnetic tape or a hard disk drive); andoptical storage media (including, for example a CD, a DVD, or a Flu-rayDisc). Examples of the media with a built-in rewriteable non-volatilememory, include but are not limited to memory cards; and media with abuilt-in ROM, including but not limited to ROM cassettes; etc.Furthermore, various information regarding stored images, for example,property information, may be stored in any other form, or it may beprovided in other ways.

The apparatuses and methods described in this application may bepartially or fully implemented by a special purpose computer created byconfiguring a general purpose computer to execute one or more particularfunctions embodied in computer programs. The functional blocks andflowchart elements described above serve as software specifications,which can be translated into the computer programs by the routine workof a skilled technician or programmer.

The computer programs include processor-executable instructions that arestored on at least one non-transitory computer-readable medium. Thecomputer programs may also include or rely on stored data. The computerprograms may encompass a basic input/output system (BIOS) that interactswith hardware of the special purpose computer, device drivers thatinteract with particular devices of the special purpose computer, one ormore operating systems, user applications, background services,background applications, etc.

The computer programs may include: (i) descriptive text to be parsed,such as HTML (hypertext markup language) or XML (extensible markuplanguage), (ii) assembly code, (iii) object code generated from sourcecode by a compiler, (iv) source code for execution by an interpreter,(v) source code for compilation and execution by a just-in-timecompiler, etc. As examples only, source code may be written using syntaxfrom languages including C, C++, C#, Objective-C, Haskell, Go, SQL, R,Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5,Ada, ASP (active server pages), PHP, Scala, Eiffel, Smalltalk, Erlang,Ruby, Flash®, Visual Basic®, Lua, and Python®.

None of the elements recited in the claims are intended to be ameans-plus-function element within the meaning of 35 U.S.C. §112(f)unless an element is expressly recited using the phrase “means for” or,in the case of a method claim, using the phrases “operation for” or“step for.”

Example embodiments being thus described, it will be obvious that thesame may be varied in many ways. Such variations are not to be regardedas a departure from the spirit and scope of the present invention, andall such modifications as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

1. A method for determining a resultant image, comprising: recording aplurality of images of a region under examination at different times;deriving anatomical information from at least one of the plurality ofimages; subsequently deriving flow information from the at least one ofthe plurality of images; and determining a resultant image, wherein anintensity-dependent fenestration assigns gray-scale values to pixels ofthe resultant image in accordance with the derived anatomicalinformation, wherein a time-dependent fenestration assignschromaticities to the pixels in accordance with the flow information andwherein the gray-scale values and the chromaticities are assignedindependently of one another.
 2. The method of claim 1, wherein therecording of at least a part of the images is contrast-medium supported.3. The method of claim 1, wherein the anatomical information is derivedin that a first projection is performed via a plurality of the imagesrecorded at different times.
 4. The method of claim 1, wherein the flowinformation is derived on the basis of a physical model.
 5. The methodof claim 1, wherein the time-dependent fenestration is performed suchthat a maximum chromaticity luminance for the pixels is the same.
 6. Themethod of claim 1, wherein the time-dependent fenestration is performedsuch that a maximum color saturation for the pixels is the same.
 7. Themethod of claim 1, wherein at least one of the gray scale for theintensity-dependent fenestration and the color scale for thetime-dependent fenestration is prespecifiable.
 8. The method of claim 1,further comprising: graphically outputting the resultant image on adisplay unit, wherein a section of the resultant image is selectable,wherein at least one of the gray scale and the color scale are dependentupon the section selected.
 9. The method of claim 1, wherein each of theimages are spatially three-dimensional images, wherein the anatomicalinformation and the flow information are both embodied as spatiallythree-dimensional, wherein the resultant image is a spatiallytwo-dimensional image, wherein the intensity-dependent fenestration isperformed such that the gray-scale values are assigned to the pixels inaccordance with the anatomical information projected along a spatialdirection, and wherein the time-dependent fenestration is performed suchthat the chromaticities are assigned to the pixels in accordance withthe flow information projected along the spatial direction.
 10. Anon-transitory computer readable medium comprising program code forperforming the method of claim 1 when the computer program is executedon a computer.
 11. A non-transitory machine-readable data carrier,storing computer program code, for performing the method of claim 1 whenthe computer program is executed on a computer.
 12. An imaging device,comprising: a computer to control the imaging device, wherein, bysending commands to the imaging device, the computer causes the imagingdevice to at least: record a plurality of images of a region underexamination at different times; derive anatomical information from atleast one of the plurality of images; subsequently derive flowinformation from the at least one of the plurality of images; anddetermine a resultant image, wherein an intensity-dependent fenestrationassigns gray-scale values to pixels of the resultant image in accordancewith the derived anatomical information, wherein a time-dependentfenestration assigns chromaticities to the pixels in accordance with theflow information and wherein the gray-scale values and thechromaticities are assigned independently of one another.
 13. The methodof claim 7, further comprising: graphically outputting the resultantimage on a display unit, wherein a section of the resultant image isselectable, wherein at least one of the gray scale and the color scaleare dependent upon the section selected.
 14. The method of claim 2,wherein the recording of at least a part of the images iscontrast-medium supported.
 15. The method of claim 2, wherein theanatomical information is derived in that a first projection isperformed via a plurality of the images recorded at different times. 16.The method of claim 2, wherein the flow information is derived on thebasis of a physical model.
 17. The method of claim 2, wherein thetime-dependent fenestration is performed such that a maximumchromaticity luminance for the pixels is the same.